As is generally known, the image quality of analog cameras, digital cameras, and the like largely depends on the performance of image sensing lenses. Since the image sensing lens of a camera such as a single-lens reflex camera called a high-end model has a large aperture size, a bright image can be obtained.
Even when the object luminance remains the same, the depth of field can be changed by variously selecting the combinations of apertures and shutter speeds and, as a result, the blur effect of objects other than a principal object can be freely controlled. The high-end model can take appealing photos for such reason.
However, a camera having a lens with a large aperture size becomes large and heavy as a whole since its image sensing lens is large. By contrast, a lens-shutter camera or the like has advantages in a small size and light weight, but its image sensing lens has a small aperture size and a large depth of field. Hence, it is difficult for such compact camera to take an image with a blur effect, which can be taken by a camera with a lens of a large aperture size.
Hence, Japanese Patent Laid-Open No. 9-181966 discloses a method of adding blur by an image process using images taken using a pair of image sensing lenses having parallax. FIG. 19 shows a concept of this conventional image processing method.
Initially, a pair of images A and B having parallax are input. The amount of image deviation of each object in the image is calculated based on these images A and B using a known correlation operation or the like, and the distance to the object is calculated based on the image deviation amount. The amount of blur of each object is calculated based on the distance information, and an image process that reproduces such blur is applied to image A or B. Upon calculating the blur amount, the operator inputs the focal length, f-number, focal point position, and the like of the image sensing lens in advance, and the blur amount is calculated based on such information together with the distance information. In this way, an image with a blur effect like that taken by a lens with a large aperture size can be generated from images taken via the lenses with a small aperture size.
However, in the above prior art, two images A and B are used to calculate the image deviation amount, and an image generated via the image process for adding blur is either image A or B. For example, in case of a digital camera, assuming that image A or B is defined by 640×480 pixels (about 300,000 pixels), an image sensing element having at least 600,000 pixels or two image sensing elements having 300,000 pixels are required to obtain two images A and B. However, the generated image with a blur effect is defined by 300,000 pixels. That is, in order to obtain an image of an arbitrary number of pixels, to which blur is added by the image process, the number of pixels at least twice that of the image to be obtained is required, and the resolution of the obtained image is limited relative to the required cost and space.
Furthermore, upon calculating the image deviation amount (distance) of each object, if an image has a low contrast, the correlation operation of the image deviation amount often results in a calculation error. However, the prior art does not consider any processing operation when such error has occurred. For example, when an object to which blur is not to be added suffers such calculation error, blur is automatically added, and an unnatural image with low image quality is output against operator's intention.